Cert Spotter is a Certificate Transparency log monitor from SSLMate that alerts you when a SSL/TLS certificate is issued for one of your domains. Cert Spotter is easier than other open source CT monitors, since it does not require a database. It's also more robust, since it uses a special certificate parser that ensures it won't miss certificates.

Cert Spotter is also available as a hosted service by SSLMate,

You can use Cert Spotter to detect: * Certificates issued to attackers who have compromised a certificate authority and want to impersonate your site. * Certificates issued to attackers who are using your infrastructure to serve malware. * Certificates issued in violation of your corporate policy or outside of your centralized certificate procurement process. * Certificates issued to your infrastructure providers without your consent.